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My PC currently has 2x1GB RAM sticks, and was considering on buying a 2GB RAM stick so that I could move it to a new PC in the future in case it was needed. Would I get the benefits of dual channel or should I necessarily buy 2x1GB sticks? (which, in a way, restricts me to 4GB of RAM if I don't want to scrap a couple of those later).

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up vote 3 down vote accepted

If you add a single 2GB module to your existing 2x1GB modules, your motherboard will probably operate all three modules in single-channel mode. For example, the ASRock P55 Extreme manual says:

If only one memory module or three memory modules are installed in the DDR3 DIMM slots on this motherboard, it is unable to activate the Dual Channel Memory Technology

If you know what motherboard your computer has, you could check its manual to be sure.

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You get the benefit of dual-channel as long as the chips in each pair are the same. I would get the 2x1GB set - that's the way most sets are sold, as well.

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From the Wikipedia article:

If the motherboard has two pairs of differently colored DIMM sockets (the colors indicate which bank they belong to, bank 0 or bank 1), then one can place a matched pair of memory modules in bank 0, but a different-capacity pair of modules in bank 1, as long as they are of the same speed. Using this scheme, a pair of 1 GB memory modules in bank 0 and a pair of matched 512 MB modules in bank 1 would be acceptable for dual-channel operation.

So, you should be fine as long as you buy the same speed RAM. However, you may want to check your motherboard manual, as there are sometimes other restrictions on what types of RAM you can use.

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